The invention relates to a set of filters for use in existing filter walls, and especially in the duct systems of ventilating installations.
In the air conditioning and ventilating field there is often a need for the cleaning of the air. Frequently the dusts involved are of relatively small quantity, but in the ventilation, for example, of electrical switchgear or of lacquer spray booths, they can be a considerable nuisance.
In German Petty Pat. 6,913,804 there is described a housing which can be inserted between sections of ventilation duct and which accommodates bag filters or pocket filters for the cleaning of air or gases. This housing is a duct section of compact construction and standardized cross section in which a high-surface-area filter of known construction is pivotingly installed, and which is installed as a complete unit in an existing system. For numerous existing systems, however, it has proven to be unsatisfactory, especially since the air ducts in a great number of cases have non-standard duct cross sections. A considerable loss of regularly usable filter area is therefore often unavoidable. A special difficulty is furthermore to be seen in the fact that, in most filters of this type of construction, it is not possible to examine newly installed filter mats for leaks, especially in the marginal areas, and such leaks can result in undetected penetration of dust.
In the effort to fill the entire cross section of existing filter walls with filter elements and at the same time assure a leakproof joining together of the filter mats, a system has become known recently in which filter elements based on standardized outside dimensions and of similar external shape are used. In these filter elements it is no longer just the filter mat that is replaced when it is dirty, but the filter medium is in the form of self-supporting pockets fastened to a head frame at their open end, and is replaced together with the head frame.
The coverage of existing areas have been improved by having, in addition to the filter element equipped with a square head frame, filter elements which are provided with a rectangular head frame which covers half of the square-shaped area of the standard frame.
Since the filter pockets of such filter elements have self-supporting properties only if they are held in an upright position, it was necessary in this system to have some rectangular elements available whose pockets are arranged parallel to the long sides of the rectangle, and some whose pockets are arranged transversely of the long sides. Nevertheless a satisfactory filtering action has not yet been achieved by means of this system. Evidently due to insufficient static and dynamic stiffening, uncontrolled fluttering and ballooning movement of the filter pockets occurred, resulting in fibers coming loose from the cut edges and in a loss of active filter surface.